Comments about adding tablet support to Wayland

[Dmitry Kazakov]

> > The situation is getting even worse if you look at the feature which
> > Windows' Wacom driver has (I'm not sure whether this feature is available
> > in X11 Wacom driver, but it is highly requested by the painters). On
> > Windows the buttons on the stylus can be switched into "modifier" mode.
> > That is pressing the button doesn't produce a real button event. You need
> > to press the  stylus button, and then touch the surface of the tablet
> with
> > the tip: only then the app will get mouse button click (right or middle
> > button usually). If this feature will ever be implemented in X11 Wacom
> > driver (which is quite desirable), your protocol with TabletTouch/Press
> > will not work. Please check Wintab protocol docs for more info,
> > specifically, CSR_SYSBTNMAP attributes [0]
>
> are you talking about Option TPCButton? it does what you describe above,
> and
> the earliest reference in the linuxwacom driver I can find for it is 2003
> :)
>

Probably, yes. How the semantic of TabletTouch/Release will work in that
case? Technically, a TabletTouch event will have to be sent on each button
pressed, won't it?





> > 3) Axes resolution. Yes, it is perfectly ok to have a separate function
> > which tells the physical limits of the axis. What I wanted to say is that
> > min_value/max_value attributes, which are reported by XInput are not
> > enough. For rotation I also need to know the mapping of the coordinate
> > system origin and it's direction (clockwise/counterclockwise).
>
> we're planning to have this well defined for the protocol so that these
> things can be relied upon.
>
> Cheers,
>    Peter
>
> >
> > PS:
> > Please keep me in CC, I'm having troubles with keeping up with the
> traffic
> > in this mailing list.
> >
> >
> > [0] - http://www.wacomeng.com/windows/docs/Wintab_v140.htm
> >
> >
> >
> > On Fri, Jun 27, 2014 at 6:53 AM, Jason Gerecke <killertofu at gmail.com>
> wrote:
> >
> > > On Wed, Jun 25, 2014 at 5:50 PM, Peter Hutterer
> > > <peter.hutterer at who-t.net> wrote:
> > > > Replying to three emails at once here to keep the thread a bit more
> > > > managable.
> > > >
> > > > On Wed, Jun 25, 2014 at 01:38:22PM -0700, Jason Gerecke wrote:
> > > >> On Wed, Jun 25, 2014 at 12:38 AM, Lyude <thatslyude at gmail.com>
> wrote:
> > > >> > On Wed, 2014-06-25 at 11:06 +0400, Dmitry Kazakov wrote:
> > > >> >> Hi, all!
> > > >> >>
> > > >> >>
> > > >> >> I am a developer from Krita painting application team. We
> recently
> > > did
> > > >> >> quite much work on incorporating better tablet support in Krita.
> I
> > > >> >> have several comments about your proposal of the tablet protocol
> > > >> >> (sorry for nor replying directly, since I wasn't subscribed to
> the
> > > >> >> list before).
> > > >> >
> > > >> > Benjamin commented on this as I was writing this e-mail, and I
> > > figured I
> > > >> > should too: yes, it's awesome to see developers commenting on the
> > > >> > protocol. A lot of the quirks around this protocol are going to be
> > > >> > difficult to see without the help of people who have programmed
> on the
> > > >> > client side of things as opposed to the compositor side of
> things. So
> > > >> > yes, your input is very much appreciated and I thank you for it!
> > > >> >
> > > >> >>
> > > >> >> 1) Axes. There should also be an axis for rotation of the stylus
> > > >> >> (Artpen) and Tangential Pressure (for the wheel of the Airbrush).
> > > >> >>
> > > >> >> 2) There is also Artpen type of stylus. In Qt it is called
> > > "Rotational
> > > >> >> Stylus".
> > > >> >
> > > >> > Don't worry, we haven't forgotten about these. These will
> eventually
> > > be
> > > >> > added into the protocol. The reason why they're not in this draft
> is
> > > >> > because I'm doing this as my Google Summer of Code project, and as
> > > such
> > > >> > I'm on a deadline and I have to focus on just getting the basics
> done
> > > >> > first before I can focus on all of the other features.
> > > >
> > > > Our current approach, both in libinput and the WL protocol should
> make
> > > these
> > > > additions little more than adding a couple of enum, so I think we're
> good
> > > > here.
> > > >
> > > >> >> 3) Fingers. There is a complication in XInput2 right now, since
> touch
> > > >> >> enabled Wacom devices have a special Finger XInput2 device, which
> > > >> >> provides both interfaces: tablet and touch and therefore
> generates
> > > >> >> both types of events. Right now Qt5 still cannot handle it
> properly,
> > > >> >> but the work is in progress. From Krita point of view, the main
> > > >> >> usecase for us is to distinguish whether the user paints with a
> > > finger
> > > >> >> of with the stylus. Because most of the users prefer to disable
> > > >> >> painting with fingers and use it for gestures/UI only (yes, palm
> > > >> >> detection works with non-100% probability).
> > > >> >
> > > >> > Right now libinput handles the finger device as another touchpad,
> > > since
> > > >> > that's usually what it is. Your use-case sounds perfectly valid
> > > though,
> > > >> > but IMO a better approach would be to add something to the
> protocol
> > > for
> > > >> > touchpads on wayland so that it can be known that they belong to a
> > > >> > tablet and provide any other sorts of data you might be need, so
> > > >> > programs like yours can treat them differently.
> > > >
> > > > Dmitry, are you talking about pen/touch arbitration, i.e. don't send
> > > touch
> > > > events when the pen is in use. If so, that's definitely on the plan,
> we
> > > need
> > > > it for touchpads (disable while typing feature), and we need it for
> the
> > > > pen/touch interference.
> > > >
> > > > This will be hidden away so you or event the compositor don't have to
> > > worry
> > > > about it.
> > > >
> > > >> >> 4) Button Press/Release events should come in both cases: when
> the
> > > >> >> user clicks on the stylus' buttons and when the stylus touches
> the
> > > >> >> surface of the tablet.
> > > >> >
> > > >> > I'm not entirely sure that's a good idea. If I'm reading this
> right,
> > > you
> > > >> > mean that additional button presses should be sent when the tool
> > > touches
> > > >> > the surface of the tablet. [...]
> > > >
> > > > We're already sending out BTN_TOUCH when the tip touches the
> surface, so
> > > I
> > > > think we're good here. Unless Dmitry was referring to something else.
> > > >
> > > >
> > > >> >> 6) It might be a good idea to define the physical properties of
> the
> > > >> >> axes. E.g. for tilt, rotation and tangential pressure. Afair,
> Wacom
> > > >> >> driver for XInput returns some not-very-obvious values right
> now. One
> > > >> >> would need to experiment to know what these numbers mean.
> > > >> >
> > > >> > We would all love for this to be the case I promise you, but
> > > >> > unfortunately it's not that simple for all of the axes. The
> distance
> > > >> > axis reports a seemingly meaningless value that can't be
> converted to
> > > >> > millimeters very easily. That being said, I have come up with a
> few
> > > ways
> > > >> > that we could actually convert it to millimeters, but this will
> have
> > > to
> > > >> > wait until I've fulfilled the goals for my Google Summer of Code
> > > Project
> > > >> > (unless anyone else wants to implement this in the mean time in
> > > libinput
> > > >> > of course).
> > > >> >
> > > >> > I'll write up the method I've come up with for converting this
> wild
> > > >> > value to actual millimeters at some point when I get the chance.
> > > >> >
> > > >> While I'm interested in seeing what you've come up with, I would be
> > > >> very hesitant to integrate the code into libinput. We make *no*
> claims
> > > >> about the physical resolution or accuracy of the distance axis. I've
> > > >> seen the value change by more than 10 units just by switching to a
> > > >> different pen... There's absolutely nothing stopping us from
> > > >> introducing a tablet that invalidates any clever code you may come
> up
> > > >> with.
> > > >
> > > > yeah, I agree with Jason here, let's not pretend we have data we
> don't
> > > have.
> > > > As much as I'd like to attach concrete physical information to all
> axes
> > > we
> > > > can't (well, shouldn't) make it up.
> > > >
> > > > Short of keeping a database of each tablet with the offsets and
> ratios to
> > > > convert distance values to mm I don't think this is doable, and I'm
> not a
> > > > big fan of that either.
> > > >
> > > >> > As for the tilt axes of the tools, this is something that could be
> > > >> > represented in a more meaningful value. We could normalize it to a
> > > >> > number between 0 and 180°, so you can get the actual tilt in
> degrees
> > > as
> > > >> > opposed to what we currently have. This is something we could
> pull off
> > > >> > rather easily, I'll make sure to discuss this with my mentor
> tomorrow.
> > > >> >
> > > >> Alternatively, I would suggest adding an e.g.
> > > >> `libinput_event_tablet_get_axis_resolution` function. To get a
> > > >> physical value, a caller would just multiply whatever this function
> > > >> returns for some axis by the current normalized unitless value for
> the
> > > >> same. I suggest this for a few reasons: it is a fairly standard way
> of
> > > >> doing things (HID, the kernel, and X all use the same system), is
> more
> > > >> efficient (callers working in your preferred unit [e.g. Qt] are
> spared
> > > >> doing the conversion but anyone else [e.g. GTK, EFL] will have to
> do a
> > > >> second conversion to a different unit), and provides a way of
> getting
> > > >> physical information for any axis (if we ever came out with a pen
> that
> > > >> accurately measured distance, you wouldn't need to change the
> > > >> semantics of how distance is reported or sacrifice the now-existant
> > > >> physical translation information).
> > > >
> > > > Jason: how accurate is tilt, and are applications actually using it
> as
> > > angle or
> > > > just as normalized number anyway?
> > > >
> > >
> > > I can't find a mention of the accuracy in any public docs, so I'm a
> > > little hesitant to give numbers on the list. The spec sheet does show
> > > it to be accurate to a handful of degrees though.
> > >
> > > The second part is a little complicated to answer. Every tilt-enabled
> > > program I'm aware of uses the data to adjust the brush azimuth. The
> > > goal is to have the virtual brush angled to be parallel with the
> > > physical pen at all times. A few applications also calculate an
> > > altitude angle, deforming the brush from circular to increasingly
> > > eliptical as the pen becomes more horizontal. Qt and Android (and
> > > likely EFL based on current discussions) have APIs that specify angles
> > > in various physical forms: tilt-x/tilt-y in degrees, alt-az in
> > > radians, etc. GTK on the other hand provides normalized data, but
> > > neither provides resolution information nor information about what
> > > "normalized" means. Because of the resulting ambiguity, GIMP and
> > > Inkscape do their calculations on the assumption that [-1, 1] in GTK
> > > corresponds to [-180 degrees, +180 degrees] in the physical world. GTK
> > > actually does its normalization based on the device's min/max though
> > > (so [-64 degrees, +63 degrees] for our hardware) meaning that GIMP and
> > > Inkscape wind up calculating incorrect azimuth values. The results
> > > aren't _that_ wrong though; I'm not aware of anyone having noticed or
> > > filing a bug about it.
> > >
> > > tl;dr, Applications universally /try/ to use the physical angles. Not
> > > all succeed.
> > >
> > > Jason
> > > ---
> > > Now instead of four in the eights place /
> > > you’ve got three, ‘Cause you added one  /
> > > (That is to say, eight) to the two,     /
> > > But you can’t take seven from three,    /
> > > So you look at the sixty-fours....
> > >
> > > >> > As for tangential pressure, this is a term I've never actually
> heard
> > > of
> > > >> > before. I don't know what the values from the tablet are supposed
> to
> > > >> > correspond to in regards to pressure, so I've added two of our
> friends
> > > >> > at Wacom to the CC list help us out (I hope you two don't mind!)
> on
> > > >> > this.
> > > >> > (Jason and Ping, if you guys aren't on the list already, the
> original
> > > >> > protocol this e-mail is discussing can be found here:
> > > >> >
> > >
> http://lists.freedesktop.org/archives/wayland-devel/2014-June/015583.html
> > > >> > )
> > > >> >
> > > >> > In regards to rotation and any other axes, I haven't had any
> contact
> > > >> > with these yet. So I can't really say much on them.
> > > >
> > > > Rotation exists on the mouse/lens cursor tool, but it's a calculation
> > > based
> > > > on the tilt x/y axes. For us it'd just be one more axis.
> > > >
> > > > Cheers,
> > > >    Peter
> > > >
> > > >> I'm not sure where the term "tangential pressure" came from, but it
> > > >> can refer either to the fingerwheel on the airbrush tool (expected
> to
> > > >> be used to control ink flow rate; value is basically [0, 1]) or the
> > > >> fingerwheel on the 4D Mouse tool (which is like a spring-loaded
> > > >> mousewheel that reports how far forward or backward from the neutral
> > > >> position the wheel is; value is basically [-1, 1]).
> > > >>
> > > >> Jason
> > > >
> > >
> >
> >
> >
> > --
> > Dmitry Kazakov
>



-- 
Dmitry Kazakov
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/wayland-devel/attachments/20140701/04648993/attachment-0001.html>